C) – and my bet is it would not be a first baseman, unless both Carpenter and Martinez were also injured. Even then, they have Gyorko and Molina in reserve. The odds of all three (Voit, Carpenter and Martinez) being hurt at the same time are pretty low.
Further, the roster would still be a problem. If Voit is injured and out for the year in Memphis, he would have to be promoted to St. Louis before being placed on the 60-day DL. That has significant financial implications.
You may not have noticed that they are in that exact place with Sherriff right now. I bet they would like to use his 40-man roster spot, but cannot easily do so.